Apparatus for introducing a reactive chemical into the pilot zone of a combustion chamber



I Jan. 16, 1962 R. L. DUNCAN ETAL 3,016,704

APPARATUS FOR INTRODUCING A REACTIVE CHEMICAL INTO THE PILOT ZONE OF A COMBUSTION CHAMBER Filed June 25, 1959 EXHAUST- 4 FROMMAIN m BURNER- INVENTORS RICHARD L. DUNCAN DAVID J. M/LLER FRANK R. CALDWELL F/LLMER I RUE 66' ERNEST E FIOGK United States Patent Ofifice 3,016,704 Patented Jan. 16, 1962 APPARATUS FOR INTRODUCING A REACTIVE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an apparatus and method for improvement of aircraft and missile performance and more particularly to an apparatus and method for improvement of jet engine and ram jet performance in which a reactive chemical is introduced into the pilot combustion zone of a combustion chamber.

Performance of jet engines and ram jets, especially at high altitudes, is seriously affected by ignitability; flame stability, involving effects of velocity, pressure and mixture ratio on flameout; and combustion efficiency. For.

example, even though ignition of an afterburner has been achieved at a lower altitude, if flameout occurs after an ascent it may be impossible to reignite without descending to a lower altitude. Hence, both ignitability and flame stability, or maintenance of flame at the higher altitudes.

can be seen to be of primary importance. Operation of the afterburner at high combustion efliciency is of equal importance because superposition of a low combustion efliciency upon the already high specific fuel consumption of the afterburner can seriously limit the range of aircraft using the afterburner to any appreciable extent.

Prior methods of improving engine performance have involved the use of complex fabricated shapes which include provisions for adequate fiameholder blockage, long fuel mixing lengths, low burner inlet velocities and large.

volume. Even with these provisions burning is often erratic and ignition diflicult except with rich fuel-air mixtures. Other attempts have included adding additives to the fuel; however, the resulting improvement in performance has not been found adequate to offset the increased.

cost of operation. Similarly, the injection of oxygen into the burner upstream from the flameholder has not resulted in any appreciable increase in engine efliciency.

The present invention proposes the introduction of additives into the primary and local zones of combustion of jet engines and ram jets to provide energy to sustain combustion under adverse operating conditions. More particularly, by introducing a quantity of a highly reactive chemical such as ethylene-oxide, oxygen, hydrogen, hydrogen peroxide or the like into the combustion zone, combustion can be initiated and sustained in combination with conventional jet fuels and conventional combustion chamber structures under conditions heretofore considered prohibitive of effective engine performance. Not only does the invention improve flame stability, ignitability and combustion efliciency of existing jet engines and ram jets, but a small quantity of the reactive chemical (often less than 1% of airflow) can be substituted for the present complex mechanical shapes and large combustion volumes which have been considered necessary to the improvement of engine performance.

Accordingly, an object of the present invention is the provision of a system for improving jet engine and ram jet performance.

Another object is to provide a system for improving ignitability, flame stability and combustion efficiency' of jet engines and ram jets operating under adverse conditions.

Still another object of the invention is to provide a system for improving the performance of existing combustion chambers and afterburner configurations.

A further object is to provide a system of improving jet engine and ram jet performance under adverse operating conditions by using a reactive chemical in place of complex mechanical shapes and large combustion volumes.

Another object of the invention is to provide a method of improving jet engine and ram jet performance by introducing a reactive chemical into the pilot combustion zone.

A final object of the invention is to provide an apparatus utilizing a simple additive introduction system and non-complex flameholders for initiating and sustaining combustion in jet engines and ram jets operating under adverse conditions.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a cross-sectional, schematic view of the burner system comprising the instant invention;

FIG. 2 is an end view of the fuel and chemical injection ring; and

FIG. 3 is a modified embodiment of a fiameholder and chemical injection ring.

Referring to FIG. 1 there is shown an afterburner 4 having a combustion chamber 5 which receives the exhaust gases from the main burner (not shown). Fuel is injected into the combustion gases in a downstream direction by the fuel injector 6 which, as shown in'FIG. 2, may take the form of an annular ring concentrically mounted in the combustion chamber by struts 7, fuel being introduced into the injector through inlets 8. A flameholder 9 is positioned downstream of the fuel injector, the preferred embodiment of the flameholder being a ring of wedge-shaped cross section. An injector ring 11 similar to the fuel injector 6 is mounted just below the flameholder and serves to inject a highly reactive chemical such as oxygen, hydrogen, hydrogen peroxide, ethylene-oxide or the like in an upstream direction against the flat face 10 of the flameholder.

As is apparent from the preceding description, fuel is first injected into the combustion gases of a main burner and then passes downstream to the flameholder and chemical injection ring where the fuel-gas mixture is ignited and burned. Initial ignition of the fuel-gas mixture may be accomplished by a spark to the face 10 of the flameholder by a conventional electrode or by a hot streak igniter. In a hot streak igniter a fuel injector is placed upstream from the afterburner, and when ignition of the afterburner is desired fuel is injected momentarily. The hot streak thus formed is blown downstream and ignites the afterburner when conditions are such that ignition is possible. A reactive chemical such as gaseous oxygen is injected in small quantities (less than 1% of airflow) on the downstream face of the flameholder to initiate and sustain combustion.

By use of the system of the instant invention combustion can be sustained at entrance velocities to the burner of 670 feet per second at pressures of six inches of mercury absolute and temperatures of 1200" F. with an oxygen-air ratio of 0.23%. In comparison ignition could not be obtained at pressures less than 12 inches of mercury absolute under the same conditions without oxygen injection or when oxygen was injected upstream of the flameholder. It will thus be seen that injection of a reacthrough the inside wall.

tive chemical into the combustion zone will permit operation of the afterburner at higher altitudes than heretofore possible. Further, the possibility of flameout is considerably lessened and combustion etficiency is improved.

In FIG. 3 there is shown a modified fiameholder and injection ring construction in which the ring 12 is immersed in a groove 13 in the downstream face of the fiameholder 14. The inside and outside walls of the groove 15 and 16, respectively, have a plurality of radially extending holes 17, there being approximately twice as many holes through the outside wall than The reactive chemical is injected radially against the inner wall surfaces.

The mild jets of chemical issuing from the ring 12 promote heterogeneity of the fuel and oxidant mixture since unmixed oxidant will be surrounded'by the mix ture of fuel and oxidant, thus permitting flame stability over a wide range of fuel-air ratios. Fuel and oxidant heterogeneity with the resulting enhancement of flame stability is also throught to be promoted by the entrance of the mixture through the holes into the atmosphere of oxidant in the annular cavity.

Although the method of chemical introduction has been described with reference to an annular ring, other means may be devised such as a rocket combustion chamber for use with rocket fuels as the active chemical additive, or simple cylindrical, hollow reaction chambers for decomposition of the active chemical. Further the system of the present invention is not limited to use in afterburners, but is adaptable for use in the main com bustion chamber of jet engines.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A burner system for a jet engine comprising a combustion chamber having upstream and downstream ends, fuel injection means mounted in said chamber near the upstream end thereof for injecting fuel in a downstream direction, an annular fiameholder mounted in said chamber downstream from said fuel injection means, said annular flameholder having a fiat downstream face, and an imperforate leading edge and a second injection means mounted in said chamber downstream from said flameholder, said second injection means formed by an injector ring having a plurality of radially spaced outlets positioned to direct a reactive chemical in an upstream direction against the flat face of said flameholder.

2. The system as claimed in claim 1 in which said flameholder is in the form of a ring of wedge-shaped cross section.

3. An afterburner for a jet engine comprising a combustion chamber having an upstream end for receiving the exhaust gases from the main burner of the jet engine and a downstream end for exhausting the burned gases, a fuel injection means within said chamber near the upstream end thereof for injecting fuel into the exhaust gases in a downstream direction, an annular flameholder mounted within said chamber downstream from said fuel injection means, said annular flameholder being in the form of a ring having a wedge-shaped cross section, and

an imperforate leading edge and a second injection means formed by an injector ring having a plurality of radially spaced outlets which. is mounted in said chamber for injecting a highly reactive chemical on the downstream face of said fiameholder.

4. An afterburner as claimed in claim 3 in which the downstream face of said annular flameholder is flat and in which the second injection means is positioned downstream from said annular flameholder for injecting the reactive chemical in an upstream direction against said 'fiat face.

5. An afterburner as claimed in claim 3 in which said annular flarneholder has a groove in the downstream face, said groove having outer and inner walls with a plurality of radially extending holes therethrough, said second injection means being mounted within said groove.

6. The afterburner as claimed in claim 5 in which the number of holes in the outer wall exceeds the number of holes in the inner wall and in which the second injection means is positioned to inject the chemical against the inner surfaces of said walls.

7. A burner system for a jet engine comprising a combustion chamber having an upstream and a downstream end, a fuel injection means in said chamber near the upstream end thereof, an annular flameholder mounted in said chamber downstream from said fuel injection means, said fiameholder having an imperforate leading edge, a groove in the downstream end of said flameholder, said groove having inner and outer walls, a plurality of holes in said walls wherein the number of holes in the outer wall exceeds the number of holes in the inner wall, and a second injection means in said groove for injecting a reactive chemical against the inner surfaces of said walls.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,833 Nahigyan Oct. 2, 1945 2,663,142 Wilson Dec. 22, 1953 2,715,813 Holmes Aug. 23, 1955 2,878,643 Fox Mar. 24, 1959 2,882,679 Karcher Apr. 21, 1959 FOREIGN PATENTS 161,852 Australia Mar. 10, 1955 654,122 Great Britain June 6, 1951 699,356 Great Britain Nov. 4,1953 708,530 Great Britain May 5, 1954 753,175 Great Britain July 18, 1956 805,400 Great Britain Dec. 3, 1958 

1. A BURNER SYSTEM FOR A JET ENGING COMPRISING A COMBUSTION CHAMBER HAVING UPSTREAM AND DOWNSTREAM ENDS, FUEL INJECTION MEANS MOUNTED IN SAID CHAMBER NEAR THE UPSTREAM END THEREOF FOR INJECTING FUEL IN A DOWNSTREAM DIRECTION, AND ANNULAR FLAMEHOLDER MOUNTED IN SAID CHAMBER DOWNSTREAM FROM SAID FUEL INJECTION MEANS, SAID ANNULAR FLAMEHOLDER HAVING A FLAT DOWNSTREAM FACE, AND AN IMPERFORATE LEADING EDGE AND A SECOND INJECTION MEANS MOUNTED IN SAID CHAMBER DOWNSTREAM FROM SAID FLAMEHOLDER, SAID SECOND INJECTION MEANS FORMED BY AN INJECTOR RING HAVING A PLURALITY OF RADIALLY SPACED OUTLETS POSITIONED TO DIRECT A REACTIVE CHEMICAL IN AN UPSTREAM DIRECTION AGAINST THE FLAT FACE OF SAID FLAMEHOLDER. 